Ben and Pete are astonished by the unconventional structure of this episode, in which Liberace gets the lion’s share of the running time to perform a concert “for the birds”. Will a performer doing schtick ruffle Pete’s feathers, or will he be hypnotized by Liberace’s glitz and glamour? A larger than normal episode to encompass a larger than life personality!
Sources and References:
Ben chose to mimic Pete’s use of a biopic as the primary source of information about the guest-star, which he had done on the Elton John episode. Which means that Ben mostly watched Behind the Candelabra as scripted by Richard La Gravanese and directed by Steven Soderbergh. He then consulted excerpts from the memoir by Scott Thorson that the screenplay had been based upon. However, as mentioned during the episode rundown, the trivia about Liberace ringing so false in his performance in the film Sincerely Yours that the studio canceled his contractual second film did come from his Wikipedia page.
Speaking of Liberace’s film career, here is the classic ConnectTheStars mind-map of his IMDb credits:

ERATTA: Ben absolutely pronounces Richard LaGravenese’s name wrong. He seems to have left out the penultimate E in the name, making it “LaGravense” instead of how it’s said by Charlie Rose back when LaGravenese was doing press for Bridges of Madison Country.
Ben’s information about which other Muppet guests covered “Never on Sunday” comes from perusing versions via the perennial resource of SecondHand Songs, but information about the film connection and original singer comes from the song’s Wiki entry. The bouzouki scene with the traditional Greek dancing can be seen here, and for those of you who miss the Python Perspective, the original version of “The Cheese Shop” sketch with the slightly less hectic bouzouki music — but just as annoying to Cleese’s character — can be enjoyed here.
Ben’s attribution of Jerome Kern of the writer of “I Want to Sing in Opera” and Kern’s other songs included in the Muppet Show comes from the Muppet Fandom page. SecondHand Songs has a different notation of the song’s writers, and the 1911 recording they feature there places the song firmly in the UK Spot tradition of sourcing Music Hall acts for the segment. Kern’s Wikipedia entry of songs he’s written or co-written does not include “I Want to Sing in Opera” and the respective Wiki pages for the credited writers George Arthurs and Worton David do not list the show the Muppet Wikia lists as its origin, The Siren. Luckily, all three are credited on this sheet music collection of songs from the show, as preserved by Johns Hopkins University libraries. Phew! Dodged an additional errata tag there!
So many YouTube uploads helped out with the contextualization of this extended musical sequence! Errol Garner’s first recording of “Misty” has been uploaded to YouTube from that 45; HBO’s Making of Behind the Candelabra is currently available and so you can see the original rhinestone costumes that Liberace wore, and the Allan Sherman satirical version of “Five Foot Two” has also been added to the YouTube collective, if you wish to compare it to Liberace’s “take-off”. Elsewhere than YouTube, Ben’s amusement at the scope and sequence of Chopin’s nocturnes can be partially re-experienced via their entry on Wikipedia.